Sound-generating device



vSOUND GENERATING DEVICE Filed June 16, 1926 lNVENTOR M0530 flea/an Patented Sept. 18 1928. I

' .UNITED STATES 1,684,975 PATENT OFFICE.

JOSEPH SLEPI AN, OF SWISSVALE, PENNSYLVANIA, ASSIGNOB T WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A. CORPORATION 01 PENNSYLVANIA.

SOUN D-GENERATIN G DEVICE. 1

Application filed June 16, 1928. Serial No. 116,251.

My invention relates to sound-generating devices, and it has particular reference to such loud speakers as are used in connection with public address systems, radio-signal 5 reception, and for like purposes. I

One object of my invention is to provide a loud speaker having a horn which will efficiently radiate a broad band of frequencies. I Another object of my invention is to provide a loud speaker which, althoughof small dimensions shall be as eflicient a radiator as a loud speaker provided with the long, unwieldy horns known to the prior art. Another object of my invention is toprol5 vide a loud speaker which will be capable of giving a sound output of large volume without d stortion.

Another object of my invention is to provide a loud speaker having incorporated therein a lurality of sound-generating units. A still urther object of my invention is to provide a loud speaker having an opening of such size that the lowest music frequencies will notbe reflected thereat but will be effi'ciently radiated. 1

For the reproduction of vocal and other sounds, a sound radiator is desirable which is capable of radiating equally well the sound waves of all the frequencies involved in speech m and music. 7

In a loud speaker of the usual type, comprising an electromagnetic unit, a relatively small diaphragm actuated thereby, and a horn, the shape and size of the horn are very important factors in controlling the quality of the sound output.

To secure a natural reproduction, it is necessar that the horn shall provide exactly the rig t amount of load for the diaphragm, and it is also important that it be curved in such manner as to be non-resonant to any of the frequencies reproduced. It is also essential that, for a given applied force acting on the diaphragm, the air at the throat of the horn must have a nearly uniform velocity over the acoustic-frequency range. The area of the mouth of the horn must be such that only a small part of the sound is reflected back at that point, because reflections cause aircolumn resonance and consequent accentuation of the frequency reflected;

It has been established experimentally that, for best results, the curvature of the horn must follow a definite law expressed by the equation A=A,e, in which A is the area of any section considered, A the area of a section closer to the small end than the section considered, e the base of the N apierian system of logarithms, b a proportionality factor depending on the rate of flare and m the distance axially along the horn between the two sections. It has further been established by research and experiment that the final opening or mouth of the horn should be comparable in size to one half the wave-length of the lowest frequency it is desired to reproduce, in order to prevent undesirable reflections.

A horn constructed according to these requirem'ents, while theoretically having the maximum efiiciency, is too long and cumbersome to meet with public approval.

I have accordingly constructed a loud speaker comprising a plurality of short V horns, each exponentially curved according to the wtheoretical formula, and have as sembled them into a single compact unit of comparatively small size.

In order that a complete understanding of my invention may be had, reference should be made to the following description, taken in connection with the accompanying drawings.

In the drawings, 1

Fig. 1 is a front elevational view of a preferred form of my invention,

Fig. 2 is a side elevational view thereof,

Fig. 3 is a sectional view of a modified form of my invention, corresponding to a section taken along the line IIIIII of Figure 1;

Referring to the drawings, and particularly to Figs. 1 and 2, a plurality of relatively short horns 1, 1, 1, having cross-sections which vary according to the formula previously given, are arranged with their large openings- 2, 2, 2, closely adjacent. Each horn is pro vided with an electromagnetic sound reproducing unit 3, such as a telephone receiver, or the like. Preferably, the large openings 2 are given such shape as will enable them to be closely grouped without intervening passages. This shape may be either square, as

shown, or it may be polygonal. openings may be used, but they are not as desirable as openings of polygonal shape.

In certain cases, it may be desirable toprovide a single diaphragm and actuating means Circular for all the horns, a device of this type being Y illustrated in Fig. 3. A plurality of horns are mounted on a casing 4, which contains and supports a plurality of electromagnetic as would perhaps be inferred from a consideration of Figures 1 and :5. 4': sufficient number should be provided, however, to cause substantially all sound-producing portions of the large diaphragm 6 to vibrate in unison. The number of units used will accordingly be controlled to a large extent by the manner in which the diaphragm (3 is mounted, the amount of power available for diaphragm actuation, and the proposed selling price of the finished product.

Having chosen the over-all dimensions of the large opening with reference to the wavelength of'thc lowest sound frequency it is desired to produce, the proper curvature of any individual horn may be calculated by plotting a plurality of points determined by the insertion of various values of 00 in the previously given formula. The length from front to back of the complete loud speaker may next be chosen arbitrarily, and a su i;- cient number of horns of that length are ranged with their axes parallel and their openings uxtaposed to give a combined opening of the desired dimensions.

ll am accordingly, in this manner, enabled to provide a loud-speaker of relatively small. dimensions, embodying horns of the proper curvature for best reproduction, and, at the same time, the device will have a combined mouth opening as large as could be obtained heretofore only by the use of an extremely long and cumbersome horn.

In so far as quality of reproduction is concerned, l: have been unable to detect any great difference between that afforded by a single exponentially-curved horn having a large mouth opening, and a loud speaker constructed according to my invention.

The principal advantage of my invention lies in the compactness and portability of a loud speaker constructed according to the principle thereof. Such portability and compactness is not gained at the expense of faithfulness of reproduction, however, nor is there any sacrifice in the volume of output from that which could be obtained with the long and cumbersome horns of the prior art.

Although I have described my invention as applicable to horns having straight axes, it

is believed obvious that each of the separate horns could be coiled, if desired, in order to still further reduce the over-all dimensions of the device.

Other modifications will suggest themselves to those skilled in the art, without departing from the spirit of my invention. N o limitations on my invention are therefore contemplated except such as are required by the prior art, or are expressed in the appended claims.

I claim as my invention:

1. In a sound-producing device, a plurality of exponentially curved horns having a combined mouth opening of an area comparable to the square of one half the wave-length of the lowest frequency it is desired to produce.

2. In a sound-producing device, a plurality of exponentially curved horns having a combined mouth opening equal in area to the square of one-half the wave-length of the lowest frequency it is desired to produce.

in a sound-producing device, a plurality of tapering horns having polygonal outlets, said. horns being arranged. with their outlets so jun'taposed as to form substantially a single opemn in a sound-producing device, a plurality of horns arranged with their large openings in substantially a single plane, the combined area of said mouth openings being comparable to the square of one-half the wave-length of the lowest frequency it is desired to produce.

5. in a soundproducing device, a plurality of short hornshaving an. exponential curvature, said horns being so arranged as to have substantially the same characteristics as a single exponentially curved horn with a mouth opening equivalent in area to the combined mouth openings of the short horns.

"6. In a sound-producing device, a plurality of tapering horns arranged with their large openings adjacent, the said large openings having such shape that a substantial portion of the perimeter of each opening is in contact with the perimeter of an adjacent opening.

7. In a sound-producing device, a plurality of tapering horns defining air columns successive cross-sections of which are related exponentially, and means for agitating each air column, the combined area of the large openings of said horns being comparable to the square of one half the wave length of the lowest frequency it is desired to produce.

In testimony whereof I have hereunto subscribed my name this 1th day of June, 1926.

. JOSEPH SLEPIAN. 

